The present invention relates to a device for performing a plurality of operations on a workpiece, and more particularly to a device having a combination tool holder for performing a drilling operation simultaneously with one or more machining operations.
There are a great many operations in the manufacture of extremely small articles such as, for example, the point of a ballpoint pen, which involve what is generally known as "micromachining" operations. These operations generally require tools and fixtures which are capable of maintaining unusually high degrees of precision together with the capability of maintaining the precision with repeated accuracy during mass production operations.
One such tool of the prior art employed in the manufacture of ballpoint pen tips provides a socket drill and two additional tools in proper relationship to machine the outer surface of the point. The tool holder generally provides a separate drill holder shaft that is a slip-fit into the tool head body, and locked by a setscrew. The drill is also a slip-fit in the drill holder shaft bore, and also is secured by means of a setscrew. These slip-fits have tendency to cause a problem in that 1/10,000 of an inch off center at each area can result in up to four times that in the ballpoint socket, creating problems with tool life and with writing quality in the finished product. While attempts are generally made to keep the sliding fit errors under control, it is generally difficult to obtain tool blanks which may be held with the required accuracy. In many instances, the variations are compensated by grinding the drill point diameter undersized, and radially repositioning the drill holder combination by trial until the errors cancel each other, to the extent that an acceptable product is achieved.
With any slip-fit, setscrew mounting there is a related problem in a reduction of tool rigidity in that there is only line contact on one side of the holder shaft or drill shank and only point contact on the opposite side where the setscrew is located allowing flex and vibration, two known enemies of precision machining in the micromachining art.
It is therefore an object of the present invention to provide a device for performing a plurality of operations on a workpiece of microdimension which provides increased precision over those devices of the prior art.
Another object of the invention is to provide a device of the above-mentioned type which is simple to manufacture and easy to employ.
Another object of the invention is to provide a combination tool holder for performing a plurality of operations on a microdimensioned workpiece which contains a drill bit and wherein the drill bit is retained with a minimum of flex and vibration.
Yet another object of the invention is to provide a combination tool holder of the above type wherein the drill bit is retained in a more rigid manner than those devices of the prior art.